想画一个边际税率图，代码是：
N <- 120
x <- (0:N)*1000
m <- sapply(x, TaxRate1994)
par(mai=c(2,0.5,0.5,0.5))

plot(x/1000, slope(m,x), ylim=c(0,0.5),type="l",
     main="China's marginal tax rates in 1994, 2011 and 2018 (price constant)",
     xlab="Taxable Income (in thousands)",
     ylab="Income Tax Rate",
     lty=4,lwd=1, col="red", xaxt="n",yaxt="n")
axis(1,at=c(0,20,40,60,80,100,120))
axis(2,at=c(0,0.1,0.2,0.3,0.4,0.5,0.6))


但是画出来变成这样：



尝试把点变多，
N <- 120000
x <- (0:N)
m <- sapply(x, TaxRate1994)
names(TaxRate1994)
par(mai=c(2,0.5,0.5,0.5))


却变成了下面这样：

我想要的图是这样的：


请问有没有大神能帮忙呀！研究了好久都没研究出来